1. Field of the Invention
The present invention relates to organic optoelectronic devices, and more particularly, relates to a photocurrent multiplication device comprising a photocurrent multiplication phenomenon brought about by a photoconductive organic semiconductor and a light-light conversion device additionally including an organic electroluminescent layer for obtaining light-light converted light, and relates to methods for producing such devices.
2. Background Art
In the past, a photocurrent multiplication phenomenon exhibiting a photocurrent quantum yield exceeding ten thousand has been reported to occur in a device including a vacuum-evaporated film made of an organic pigment as a photocurrent multiplication layer and two metal electrodes sandwiching the photocurrent multiplication layer (see M. Hiramoto, T. Imahigashi and M. Yokoyama, Appl. Phys. Lett., 64, 187 (1994)).
However, such a photocurrent multiplication phenomenon occurring in an organic material has been observed only in a device using an organic thin film formed by vacuum evaporation as a photocurrent multiplication layer.
Also a light-light conversion device has been reported, in which an organic electroluminescent (organic EL) film is formed integrally on a photocurrent multiplication layer made of an organic pigment for performing light wavelength conversion and light amplification (see T. Katsume, M. Hiramoto and M. Yokoyama, Appl. Phys. Lett., 64, 2546 (1994), and M. Hiramoto, T. Katsume and M. Yokoyama, Opt. Rev., 1, 82 (1994)). In this case, also, the photocurrent multiplication layer is made of a vacuum-evaporated film of an organic pigment.
The conventional organic thin film formed by vacuum evaporation as the photocurrent multiplication layer has the following problem. Pinholes tend to be generated due to non-uniformity of the film, and this increases the probability of occurrence of conduction between the upper and lower electrodes. For this reason, it is difficult to increase the area.
Moreover, the vacuum evaporation method employed for formation of the photocurrent multiplication layer requires use of a large-scale apparatus for vacuuming.
The first object of the present invention is to provide a multiplication device, such as a photocurrent multiplication device and a light-light conversion device, in which conduction between upper and lower electrodes occurs less easily and thus increase of the area is possible.
The second object of the present invention is to provide a method for producing such a multiplication device easily.